One type of liquid containing device which is used in conjunction with an engine is an integrated drive generator (IDG). An IDG is a hydraulically controlled electrical generator which is mounted to an aircraft engine and driven by the engine. The IDG is designed to operate successfully in any aircraft attitude. It is also designed to be internally sealed from ambient atmosphere during operation. The IDG is filled to a predetermined level with a liquid lubricant and coolant such as oil by pressure filling through a pressure fitting and fill passage of the device until the liquid begins to spill from an overflow drain passage provided in the device. The spilling of the liquid indicates that the "full" IDG liquid level has been attained. If the overflow drain passage of the IDG is plugged, as for example where the operator neglects to remove a drain plug in the drain passage during filling, the IDG may be over-filled with liquid, causing excessive liquid thrashing losses and heat generation during operation which can damage the IDG components.
Another potentially serious problem associated with the aforementioned type liquid containing device occurs where the drain plug is removed from servicing the IDG and is not replaced. In such a case, liquid can spill out of the overflow drain, especially during aircraft flight maneuvers. The liquid loss can result in damage to the IDG and is a potential fire hazard where a flammable liquid such as oil comes into contact with hot engine components.
A liquid containing device is known from U.S. Pat. No. 3,924,708 wherein respective ball valves are provided in supply and drain passageways of the device. The ball valves are normally biased in a closed position by means of springs. This device is disadvantageous because a special, external coupling member is required to open the valves for adding and draining liquid from the device. Liquid control devices are also known from U.S. Pat. Nos. 2,617,495; 3,575,533; 4,569,196 and 4,589,524.